JPH01141410A - Sawtooth wave control circuit - Google Patents

Abstract

PURPOSE:To always cause the amplitude of a sawtooth wave to be constant by connecting a circuit to by-pass a current to be charged to a capacitor and applying a feedback so as to control the quantity of the current by-passed in proportion to the wave height value of the generated sawtooth wave. CONSTITUTION:When a frequency(f) to open and close a switch S1 is changed in a high direction, the amplitude of the sawtooth wave generated in a capacitor C1 intends to be small. A voltage, in which the sawtooth wave is integrated by a diode D1 and a capacitor C2, is made small, the output voltage of an error amplifier 2, in which the difference between the integrating voltage and a reference voltage VCC is amplified, is also made small, and the base voltage of a transistor TR1 is also made small. For such a reason, the collector current of the transistor TR1 is decreased, the charging current of the capacitor C1 is increased, and it intends to enlarge the amplitude of the sawtooth wave. The output voltage of the error amplifier 2 is continued to be increased until the integrating voltage of the capacitor C1 and the reference voltage VCC are made equal, and it is stabilized when they are made equal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sawtooth wave control circuit that can be used in circuits that require sawtooth waves of constant amplitude in general electronic equipment, including television receivers.

Conventional technology Generally, when obtaining a sawtooth υ wave, a capacitor is used, a switch circuit is connected in parallel to the capacitor, and the capacitor is charged and discharged to obtain a sawtooth voltage across the capacitor.

Problems to be Solved by the Invention However, the sawtooth wave obtained by charging and discharging a capacitor has a problem in that when the frequency of the sawtooth wave changes, the amplitude changes depending on the frequency.

The present invention provides a control circuit that can always obtain a sawtooth wave with a constant amplitude even if the frequency changes or even if the amplitude tends to change due to some factor.

Means for Solving the Problems In order to achieve the above object, the sawtooth wave control circuit according to the present invention connects a circuit that charges a capacitor and bypasses the Lumi current, and generates a sawtooth wave in proportion to the peak value of the generated sawtooth wave. It is characterized by applying feedback to control the amount of bypassed current so that the amplitude of the sawtooth wave is always constant.

According to the present invention, if the amplitude of the sawtooth wave changes due to some factor, the bypass current of the capacitor charging current changes in accordance with the change, so the amplitude of the sawtooth wave remains constant. .

Example Embodiments of the present invention will be described below with reference to the drawings.

In the figure, 1 is a constant current source, C4 is a capacitor that creates a sawtooth wave, S is a switch, TR4 is a transistor connected to both ends of capacitor C1 and forms a bypass circuit, and C2 is a voltage across capacitor C1 ( A diode and a capacitor rectify and smooth the sawtooth wave voltage, and 2 is an error amplifier, with VO at the -input terminal. Connect the reference voltage source of
A diode D1 is connected to the input terminal. A DC voltage from capacitor C2 is input. Then, the output signal of this error amplifier 2 is applied to the base of the transistor TR10.

In the above configuration, a constant current output from the constant current source 1 is passed through the capacitor C1 to charge the capacitor C1, and by opening and closing the switch S1 parallel to the capacitor C1 at a certain frequency f, a sawtooth wave is applied to the capacitor C4. Voltage is generated. Now, if the frequency f for opening and closing the switch S1 is changed in a higher direction, the amplitude of the sawtooth wave generated in the capacitor C1 tends to become smaller. Then, the voltage obtained by integrating the sawtooth wave by the diode D and the capacitor C2 becomes smaller, the output voltage of the error amplifier 2 that amplifies the difference between this integrated voltage and the reference voltage vC6 also becomes smaller, and the base voltage of the transistor TR1 also becomes smaller. . Therefore, the collector current of transistor TR1 decreases and capacitor C
The charging current of 1 increases to increase the amplitude of the sawtooth wave. The output voltage of the error amplifier 2 continues to increase until the integrated voltage of the capacitor C2 and the reference voltage v0° become equal, and becomes stable at the time they become equal. Therefore capacitor C
For the amplitude of the sawtooth wave at both ends of 1, the integrated voltage of capacitor C2 is the reference voltage V. . Since it is stable at an amplitude equal to
The amplitude of the sawtooth voltage across the capacitor C1 in a stable state before the frequency f is increased is equal to the amplitude of the sawtooth voltage across the capacitor C1 in a stable state after the frequency is increased.

On the other hand, when the frequency is lowered, the sawtooth voltage of the capacitor C1 tends to increase. Then, the voltage of the capacitor C2 becomes high, the output voltage of the error amplifier 2 also becomes high, and the pace voltage of the transistor TR1 becomes high. Therefore, the collector current of transistor TR1 increases, the charging current of capacitor C1 decreases, and the sawtooth wave voltage of capacitor C1 is tried to be reduced. becomes stable.

In this way, the amplitude of the sawtooth wave voltage of the capacitor C1 is always kept constant because feedback is applied to prevent the change in the peak value when the peak value is about to change due to changes in the frequency of the sawtooth wave or other factors.

Effects of the Invention As described above, according to the present invention, a sawtooth wave having a constant amplitude can always be obtained even if the frequency of the sawtooth wave is changed.

[Brief explanation of the drawing]

The figure is a circuit diagram of a sawtooth wave control circuit in one embodiment of the present invention. S: Switch, C1: Charge/discharge capacitor that generates a sawtooth wave, TR1:
Transistor, Dl...Diode, C2...
... Capacitor, 1 ... Constant current source, 2 ...
...Error amplifier.

Claims (1)

[Claims] The capacitor is charged and discharged using a constant current source so that a sawtooth voltage is generated across the capacitor, and a means is provided for bypassing the charging current of the capacitor in proportion to the peak value of the generated sawtooth wave. Sawtooth wave control circuit.